Electrodeposition

ABSTRACT

A METHOD OF ELECTRODEPOSITING A COATING ONTO SUBSTRATE FROM A BATH OF COATING PARICLES SUSPENDED IN AN ELECTRICALLY INSULATING LIQUID BY IMMERSING THE SUBSTRATE EITHER WHOLLY OR PARTIALLY INTO THE BATH. A PAIR OF ELECTRODES ARE PROVIDED ON EITHER SIDE OF THE SUBSTRATE BUT INSULATED FROM IT. ONE ELECTRODE MAY CONTACT THE BATH, FOR INSTANCE IT MAY LIE INSIDE THE CONTAINER OR BE THE CONTAINER. THE OTHER ELECTRODE IS SUPPORTED OUTSIDE OF THE BATH. A POTENTIAL IS APPLIED TO THE ELECTRODES SUFFICIENT TO CAUSE A CORONA DISCHARGE THROUGH THE BATH WHEREBY THE PARTICLES ARE ELECTROPHORETICALLY MOVED TO AND DEPOSITED ON THE SUBSTRATE.

y 1972 MASAMICHI SATO 3,67 ,543

ELECTRODEPOSITION Filed Aug. 18, 1970 3 Sheets-Sheet 1 INVENTOR xi/(51%)?) (2m ATT BET AVAILABLE COPY July 4, 1972 MASAMICHI SATO 3,674,543

ELECTRODEPOSITION Filed Aug. 18, 1970 5 Sheets-Sheet I/l/l/l I/l/I/ I N V E N T O R Mas/4w 04/ 5 470 y 1972 MASAMICHI SATO 3,674,543

ELECTRODEPOSITION Filed Aug. 18, 1970 3 Sheets-Sheet I5 W wges United States Patent rm. (:1. min; /02

US. Cl. 117-93 7 Claims ABSTRACT OF THE DISCLOSURE A method of electrodepositing a coating onto a substrate from a bath of coating particles suspended in an electrically insulating liquid by immersing the substrate either wholly or partially into the bath. A pair of electrodes are provided on either side of the substrate but insulated from it. One electrode may contact the bath, for instance it may lie inside the container or be the container. The other electrode is supported outside of the bath. A potential is applied to the electrodes sufiicient to cause a corona discharge through the bath whereby the particles are electrophoretically moved to and deposited on the substrate.

The instant invention pertains to a novel and highly practicable method of electrodeposition in which the electrostatic induction of solids in an electrically insulating liquid is utilized.

in order to cover or coat the surface of article by electrodeposition, there are generally a method in which an electrically conductive liquid is used as the electrodeposition liquid and a method in which an insulative liquid is used. The former requires a large amount of electric current owing to the conductivity of the electrodeposition liquid, while in the latter only a very small amount of electrocurrent is consumed owing to the low conductivity of the electrodeposition liquid.

The latter method is described in, for example, the specification of Japanese Patent Publication No. 11,415/ 1961. According to the method described in the patent, the electrically insulating liquid contains pigment particles, a charge controlling agent, and a binder agent that coat the pigment particles or is dissolved or dispersed in the insulating liquid. An article to be coated is immersed in the deposition bath as an electrode and an electric potential is applied between the electrode of the article and another electrode disposed in the bath, whereby pigment particles are attracted onto the surfaces of the article by the action of electrophoresis.

However, by such a known method, it is difiicult to electrodeposit pigment particles selectively onto the only one side of the article and also it is necessary to connect a wire to the article for supplying thereto electric current. Furthermore, such a conventional method is accompanied with a demerit that the electrode is stained caused by the contact with the electrodeposition bath.

The invention will now be described by referring to the accompanying drawings, in which FIG. 1 is a schematic cross-sectional view showing a mode of electrodeposition that has most generally been employed.

FIG. 2 is a schematic cross-sectional view showing an embodiment of the electrodeposition method of the instant invention.

FIG. 3 is a schematic view showing the principle of the electrodeposition method of this invention.

FIGS. 4-9 are cross-sectional views each showing other embodiment of the electrodeposition method of this invention.

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Now, in FIG. 1 that is a schematic cross-sectional view of the simplest example of conventional electrodeposition methods, particles 10 which may be solids, emulsion, emulsoid, colloid or high molecular weight material are suspended or dissolved in a liquid 11 by a conventional means such as a 'kneading or dispersing treatment usually employed in the production of paints or inks. The liquid 11 is a liquid or a liquid mixture having comparatively high electric resistance and is in an insulating vessel 12. An electrode 14 is immersed in the liquid with a proper interval with an electrode 13 that is also immersed in the liquid. When an electric potential is applied between the electrodes 13 and 14 (usually SOD-100,000 volts), the par ticles 10 are attracted to the electrode 14 by the action of electrophoresis if the particles are charged positively and a thick deposition is formed on the electrode 14. However, by such a conventional method the deposition is comparatively thicker in the side of the electrode 14 having to the electrode 13 but comparatively thinner at the opposite side thereof. Thus, by the method as shown in FIG. 1, the deposition becomes uneven and the whole surfaces of the electrode are coated by the electrodeposition.

Therefore, an object of this invention is to provide an electrodeposition method without the above-mentioned demerits, that is to say, an electrodeposition method than can deposit onto either only one side or the whole sides of an article to be deposited or coated and that it is not required to connect a wire to the article to be deposited, which results in avoiding the electrode from being stained.

The above-mentioned object of this invention can be attained by the electrodeposition method of this invention which comprises disposing a corona discharging electrode at the outside of an electrodeposition bath prepared by incorporating particles in an electrically insulating liquid, said particles being able to move freely in the liquid, together with, if necessary, a charge-controlling agent in the state of coating said particles or being dissolved or suspended in the liquid, a dispersion stabilizer, and a binder; placing an article to be electrodeposited between said corona discharging electrode and an opposite electrode, said article being electrically insulated from both electrodes and also being locally or wholly immersed in said electrodeposition bath, and then applying an electric po tential between the two electrodes to cause corona discharge, whereby the particles are moved to the article by the action of electrophoresis and deposited there.

Now, the several embodiments of the electrodeposition method of this invention will be explained by referring to the accompanying figures.

FIG. 2 is a schematic cross-sectional view showing the simplest embodiment of the method of this invention. In FIG. 2, a corona discharge electrode 20 is disposed over an electrodeposition bath 11 and as the electrode, a needlelike, wire-like, knife-shaped, or strip-like electrode is used so that when a proper electric potential (usually 1,000- 100,000 volts) is applied, an extremely uneven electric field is formed to cause corona discharge.

In the embodiment shown in FIG. 2, a needle-shaped electrode 20 is used. A vessel 21 is made of a metal and has an action of the opposite electrode. An article 22 to be deposited is electrically insulated from the electrodes 20 and 21 and in this embodiment the article is a metal plate. In this example, however, the article 22 is electrically connected to the electrode 21 through the electrodeposition bath, in other words, the article 22 can be said to be connected to the electrode 21 through the resistance of the electrodeposition bath. The embodiment shown in FIG. 2 is the case where particles 10 have positive charge and a negative potential is applied to the corona discharge electrode 20. When a proper electric potential applied to the electrodes 20 and 21, corona discharge is generated at the top of the electrode 20 and corona ions are directed to the surface of the electrodeposition bath, whereby polarized charges are formed on the surfaces of the metal plate 22 and the positively charged particles are uniformly deposited to the lower surface of the metallic plate 22 having the negative polarized charge, while no particles are deposited on the upper surface thereof having the positive polarized charge.

In FIG. 3 is illustrated an enlarged cross-sectional view of the metal plate 22 in FIG. 2 for showing the principle of the method of this invention.

When an electric potential is applied between the electrodes 20 and 21 in FIG. 2, positive charge is formed on the upper surface 31 of the metallic plate 22 and negative charge is formed uniformly on the lower surface thereof by electrostatic induction. Consequently, particles having positive charge are repulsed at the upper surface but are attracted onto and deposited uniformly onto the lower surface of the metal plate, whereas no particles are deposited on the upper surface of the metal plate.

In the embodiment shown in FIG. 2', if the polarity of the electric potential to be applied to the electrodes is reversed, the charges formed on the surfaces of the metal plate 22 by electrostatic polarization are reversed, thereby the particles having positive charge are deposited on the upper surface of the metal plate, whereas no particles are deposited on the lower surface thereof.

In FIG. 2, it shall be noted that almost no particles are deposited on the walls of the vessel that acts also as the electrode.

FIG. 4 is a schematic view showing other embodiments of this invention. In the example, an article 40 to be deposited is floated on an electrodeposition bath 11, that is to say, the lower portion of the article is immersed in the electrodeposition bath and the upper portion of'the article is outside the bath. Even if a part of the article to be electrodeposited is outside the electrodeposition bath as in this embodiment, polarized charges are formed by corona discharging and particles can be deposited on the lower surface of the article. In the embodiment shown in FIG. 4, the article 40 may be electrodeposited without connecting the article to a wire while floating and moving the article. Therefore, the embodiment is suitable for mass production.

FIG. 5 is a schematic sectional view showing a practical embodiment of this invention for conducting the electrodeposition on the outside surface of a vessel 50. A corona discharging electrode 20' is disposed in the vessel 50 and the electrode is electrically insulated from the vessel 50. In the embodiment shown in the figure the vessel 50 contains no electrodeposition liquid in it but the electrodeposition liquid present outside the vessel. The vessel 50 may contain the same electrodeposition liquid. An electrodeposition bath is placed in other vessel 21 which acts as an opposite electrode and the vessel 50 to be deposited is immersed in the electrodeposition bath as shown in FIG. 5. When an electric potential is applied between the corona electrode and the vessel 21, corona discharge is generated and the particles are deposited on the outside surface of the vessel 50.

FIG. 6 is a schematic cross-sectional view showing a practical embodiment of the method of this invention in which the inside and the outside surfaces of a vessel 61 are simultaneously deposited by particles having different colors respectively. The vessel 61 is made of a. material through which the electrodeposition liquid are not leaked. An electrodeposition bath containing particles having positive charge is filled in vessel 21 as in the above embodiments and the vessel 61 to be deposited is immersed in the electrodeposition bath 11. Other electrodeposition bath 60 containing particles having negative charge. By applying a proper electric potential between a corona discharging electrode 20 disposed in the vessel 61 and over the electrodeposition bath 60 and the vessel 21, the particles in the both electrodeposition baths are deposited on the both surfaces of the vessel 61 simultaneously and in this case if the particles in the both electrodeposition baths are so selected that the color of the one is different from the other, the inside surface and the outside surface of the vessel 61 can be deposited by the particles of diiferent colors respectively.

FIG. 7 is a cross-sectional view showing a practical embodiment of the electrodeposition method of this invention for depositing same kind of particles onto the both sides of an article 70. The article 70* is a vertically elongated rod-shaped, plate-shaped or cylindrical one and in the embodiment the whole surfaces of the article immersed in the electrodeposition bath can be deposited by the particles.

FIG. 8 is a modification of the embodiment shown in FIG. 7. That is to say, a plate-shaped article is suspended horizontally in the electrodeposition bath by means of a conductive member 81 and is completely immersed in the bath. A corona discharging electrode 20 is disposed near the top of the conductive member 81. When an electric potential is applied to the corona discharging electrode 20 and the opposite electrode 21 to cause corona discharging, the particles are deposited on the whole surfaces of the article 80.

FIG. 9 shows still other example of the electrodeposition method of this invention. An opposite electrode 92, is disposed at the outside of an insulating vessel 91 containing an electrodeposition bath 11 and by applying a proper electric potential to a corona discharge electrode 20 and the opposite electrode 92, similar electrodeposition can be practiced.

In the above embodiment the opposite electrode is disposed at the outside of the insulating vessel but it may be placed at the inside of the vessel.

One feature of the instant invention is to use corona discharge and even if a high electric potential is applied to the corona discharge electrode, the electrodeposition is not eifected if corona discharge is not generated.

By the above detailed description it will be understood that the instant invention be a novel and highly practicable electrodeposition method.

The coatings formed by the electrodeposition may be fixed by solvent or heating and also may be hardened by utilizing a condensation polymerization after deposition.

The invention is further described practically by the following examples.

EXAMPLE 1 An electrodeposition liquid was filled in a metal vessel having a fiat bottom and an insulating frame of a hard vinyl chloride resin having a height of 1 cm. was placed on the bottom of the vessel. A metal plate having a thickness of 2 mm. was placed on the frame and in this state the depth of the electrodeposition liquid over the surface of the metal plate was 1 cm. A metal needle was disposed over the electrodeposition bath so that the top of the metal needle was disposed about 5 mm. over the level of the electrodeposition bath. An electric potential of 7 kv. was applied to the metal needle while earthing the metal vessel and after about 30 seconds, the application of the electric potential was stopped and the metal plate was withdrawn from the bath. It was observed that a uniform and thick electrodeposited film was formed on the lower surface of the metal plate. However, no deposition was observed on the upper surface of the metal plate and the walls of the vessel. The electrodeposited film thus formed was readily broken by rubbing with finger but when the metal plate withdrawn from the electrodeposition bath was placed in a vessel filled with an acetone vapor for a few tens seconds and then dried in air, a strong coating or film was formed on the surface of the metal plate.

The electrodeposition bath used above was prepared by the following manner:

G. Vinyl acetate resin 100 Zinc oxide powder 130 Acetone 100 The above-mentioned ingredients were mixed for 8 hours in a ball mill and the paste thus prepared was dispersed in 10,000 g. of kerosine having dissolved therein 90 g. of linseed oil by applying to the system ultrasonic waves of 29 kHz. of a power of 150 watts. In the electrodeposition bath, the particles had positive charge.

When a negative electric potenial was applied to the needle electrode, the particles were deposited on to the only lower surface of the metal plate as mentioned above but when a positive potential was applied to the needle electrode, the particles were deposited onto only the upper surface of the metal plate but were not deposited onto the lower surface thereof.

In addition, when a triacetyl cellulose film having a thickness of 0.5 mm. was used instead of the metal plate, almost same results were obtained. Also, almost similar results were obtained when an electrophotographic paper or an Electrofax paper was used instead of the metal plate in the above example.

EXAMPLE 2 The electrodeposition was conducted according to the embodiment shown in FIG. 7. An electrodeposition liquid was filled in a metal vessel and a metal rod was immersed locally in the liquid in the depth of 10 cm. The length of the rod above the level of the liquid was about 2 cm. and the depth of the bath from the lower end of the rod to the bottom of the vessel was about 2 cm. The rod was suspended by means of an insulating cord. A needle elec trode was disposed over the metal rod so that the end of the needle electrode was positioned about 5 mm. over the top of the metal rod. A direct current potential of +9 kv. was applied to the needle electrode while earthing the vessel and after about 20 seconds the application of the electric potential was stopped and the metal rod was withdrawn from the bath. A thick deposition was obtained on the surface of the portion of the metal rod immersed in the electrodeposition bath. The metal rod thus withdrawn was dried, placed in a vessel filled with a butyl acetate vapor for 20 seconds, and dried in air again, whereby strongly electrodeposited coating is obtained.

The electrodeposition bath used above was prepared by the following manner:

Soybean oil-modified medium oil-length alkyd resin 20 Butyl acetate 100 The above ingredients were mixed for 4 hours in a ball mill and the paste thus prepared was dispersed in 10,000

g. of kerosine having dispersed therein 50 g. of linseed oil by applying ultrasonic waves.

In addition, in the case where particles have negative charge in the electrodeposition bath as in this example, when a negative electric potential was applied to the corona discharging electrode in the embodiments shown in FIG. 4, FIG. 5, FIG. 7, and FIG. 8, the particles were not deposited on the articles to be deposited but were deposited on the walls of the vessel.

What is claimed is:

1. A method of electrodeposition which comprises disposing a corona discharging electrode at the outside of an electrodeposition bath prepared by incorporating particles in an electrically insulating liquid, said particles being able to move freely in the liquid placing an article to be electrodeposited between said corona discharging electrode and an opposite electrode, said article being electrically insulated from the both electrodes and also being locally or wholly immersed in said electrodeposition bath, and then applying an electric potential between the both electrodes to cause corona discharge, whereby the particles are moved to the article by the action of electrophoresis and deposited thereon.

2. The method according to claim 1 wherein the electrodeposition bath contains additionally a charge-controlling agent in the state of coating said particles or being dissolved or suspended in the liquid, a dispersion stabilizer, and a binder. t

3. The method according to claim 1 wherein a vessel for the electrodeposition bath is made of a conductive material and said vessel is utilized as the opposite electrode 4. The method according to claim 1 wherein a vessel for the electrodeposition bath is made of an insulating material and the opposite electrode is disposed at the outside or the inside of the vessel.

5. The method according to claim 1 wherein the article to be electrodeposited is floated on an electrodeposition bath.

6. The method according to claim 1 wherein the article to be electrodeposited is a hollow container and the inside and the outside of said article each contact a different electrodeposition bath.

7. The method according to claim 1 wherein the electrodeposited coating is fixed by treating with heat or solvent vapor.

References Cited UNITED STATES PATENTS 3,462,286 *8/ 1969 De Geest et al. 1'17-93.4 X

FOREIGN PATENTS 221,527 12/ 1957 Australia 117-93 283,545 10/1965 Australia 117-93 ALFRED L. LEAVI'IT, Primary Examiner J. H. NEWSOME, Assistant Examiner US. Cl. X.R.

ll7-93ll CD; 204-181 UNHED STATES PATENT orrier QERTEFIUCATE @i QGRREQMQN Patent N 3,6? n5 3 Dated Julv in 1.972

Inventor s S3150 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, between lines Q and 5 insert assignor to Fuji Photo Film (20.,

L td a o Signed and sealed this 19th day of December" 1972.,

(SEAL) At'test:

ROBERT GOTTSCHALK EDWARD EKLFLETCHERJK Commissioner of Patents Attesting Officer PC4050 (10'69) USCOMM-DC 60376-P69 U.5. GOVERNMENT PRINT'NG OFFICE: I569 0-366-334. 

